One small problem here....
The Go and the Rio are both OK at 15 knots, but both are getting "way too big" at anything over 20 knots.
If you are looking for really great performance, in 20 knots plus, you would normally be on a 6.0 m2 or smaller rig, and neither the Rio M or the GO 144 are going to be real "performant" with a rig of that size.
I do not understand the statement that the Rio M "sticks to the water".
I agree it's a pretty heavy board, but I've had speeds comparable to most other lighter boards when I've sailed it in 18-20 knots with a 5.6 m2 Sailworks Hucker. You just have to get all the way back on the board and into the outboard footstraps.
Hope this helps,